1. Field of the Invention
The present invention relates to an image bearing member protecting agent for protecting a surface of an image bearing member which is used for forming electrophotographic images, a production method for the image bearing member protecting agent, a protection layer forming apparatus for forming a protection layer on the surface of the image bearing member using the image bearing member protecting agent, an image forming method, an image forming apparatus, and a process cartridge.
2. Description of the Related Art
Traditionally, electrophotographic image forming forms a visible image by having charged toner adhere to a static-charged latent electric field image formed with a static charge and formed on an image bearing member which has a photoconductive layer containing photoconductive substances thereon. The visible image is then transferred onto a recording media such as paper, and given heat, pressure, or solvent gas so that the visible image is fixed on the recording media, and thus an output image is obtained.
Classifying such image forming based on the toner charging process for visible image forming, developing process of electrophotographic is divided into two types of processes: a two-component developing process wherein frictional electrification generated through mixing and stirring toner particles and carrier particles is employed, and an one-component developing process wherein toner is charged without carrier. The one-component developing process is further divided into two categories: a magnetic-one-component developing process and a non-magnetic one-component developing process, based on whether or not magnetic force is used for keeping toner on a development roller.
Because the two-component developing process has higher stability of charge property, faster rising time, and more advantageous in maintaining high quality image over a long-period of time than the one-component developing process, the two-component developing process is widely used for complex units and copier-based complex units which require high-speed and high image reproducibility. On the other hand, for small printers and fax machines, as they need to be downsized and produced at low cost, the one-component developing system is widely adopted.
Recently, demands of better image quality and higher stability of image quality in both component developing systems increase accompanying with the spreading popularity of color image output. In order to obtain better image quality, the average particles diameter of toner is becoming smaller and the particles shape of toner is getting rounder with no angulate parts.
An electrophotographic image forming apparatus of any component developing system generally rotates an image bearing member, which is generally drum-shaped or belt-shaped, to uniformly charge the image bearing member, forms a latent image pattern on the image bearing member using, for example, laser beam irradiation, visualizes the latent image pattern into a toner image using a toner, and then transfers the toner image on a recording medium. Toner components may remain on the surface of the image bearing member after the toner image has been transferred to the recording medium. The remaining components will prevent uniform charging on the image bearing member during a charging step, and therefore, the surface of the image bearing member will be charged after removing the remaining components and cleaning the surface thereof with a cleaning unit using such as a cleaning blade.
Different kinds of electrical stresses and physical stresses given in steps such as charging, developing, transferring and cleaning steps, on the surface of the image bearing member change the surface over a period of time. Of those stresses, frictional stress generated at the cleaning process causes abrasion of the image bearing member and scratches on its surface. To solve this problem, or to reduce the friction between the image bearing member and cleaning blade, there have been various proposals regarding lubricants, supply of lubrication components and lubrication forming methods.
To prolong the life period of the photoconductor and cleaning plate, for example, Japanese Patent Application Publication (JP-B) No. 51-22380 proposes a lubrication film forming method wherein a lubrication film can be created on the surface of the photoconductor by supplying thereon a solid lubricant which mainly consists of zinc stearate.
Japanese Patent Application Laid-Open (JP-A) No. 2005-274737 proposes using a lubricant supply unit, which provides lubricant having higher alcohol of 20 to 70 carbon atoms. The higher alcohol provided from the unit stays in form of amorphous particles at the edge of blade nip member, providing adequate wet condition on the surface of the image bearing member and enabling maintaining lubrication property.
JP-A No. 2002-97483 proposes using powder of an alkylene bis alkyl acid amide compound as a lubrication component, and using the compound provides powder in the surface boundaries between an image bearing member and a cleaning blade in a contacting condition with the image bearing member, providing smooth lubrication effect on the surface thereof for a long period.
As mentioned above, stresses on the image bearing member are generated from not only the cleaning step but also from other steps, and particularly a charging step generates an electrical stress which greatly changes the surface condition of the image bearing member. The electrical stress strongly appears especially in a contact-charging system and a proximity-charging system which is accompanied by discharging phenomenon occurred near the surface of the image bearing member. Those types of charging systems generate active species and reaction products at the surface of the image bearing member, and have large occurrence of adhesions of the active species and reaction products, which are generated in the discharging area atmosphere, to the surface of the image bearing member.
Thus, although a type of lubricants, such as the lubricant of above mentioned JP-B No. 51-22380, using zinc stearate can uniformly cover the surface of an image bearing member and provide preferable lubrication thereon, zinc stearate of the lubricants may be dissolved and finally remain at the surface of the image bearing member and/or the surface of charge member in the form of zinc oxidizes over a period of time when lubricants are repeatedly exposed to charging step. The zinc oxidizes remaining at the surface have moisture-absorption characteristics and they absorb moisture existing in air with reducing resistance, so a static charge cannot be kept on the image bearing member under a high-humidity condition, and thus that may cause obscureness of a latent electric field image and an image failure, resulting in an occurrence of grainy images.
Lubricants containing higher alcohol, such as lubricant of above-mentioned JP-A No. 2005-274737, will be easily spread on the surface of the image bearing member and can be expected to have lubrication efficiency, however, adsorption area per one molecule of higher alcohol adsorbing to the image bearing member tends to be larger, reducing the density of particles adsorbing to the unit area of an image bearing member, or the adsorption molecular weight per the unit area, and the above-mentioned electrical stress can easily pass through the protection layer, thus enough protection for the image bearing member will be hard to be achieved.
A lubricant having nitrogen atoms in molecules therein, such as the lubricant of the above-mentioned JP-A No. 2002-97483, itself may generate decomposition products having ion-dissociative property, like nit oxides and ammonium-containing compounds, when electrical stress is applied thereon. The products are then contained into a lubrication layer, reducing resistance under a high-humidity condition and may result in occurrences of grainy images.
Prolonging the life period of image forming apparatus and members therefor has drawing high interest in the market in terms of lowering running cost and reducing waste products for protecting the earth's environment. For example, an approach has been tried to prolong the life period of image bearing member through increasing mechanical durability through covering the surface of an image bearing member with a particular surface layer having cross-linked structures. (See JP-A No. 2004-302451)
As mentioned above, once low resistance substances are incorporated into the lubrication layer of the image bearing member, removing those substances requires removing the entire lubrication layer with, for example, a cleaning mechanism, and because of the slippery surface of the lubrication layer, removing requires great force and gives great amount of mechanical stress on the image bearing member itself. Thus, even covering the surface of the image bearing member with the particular surface layer having cross-linked structure, as of above mentioned JP-A No. 2004-302451, has not drastically changed the life period of the image bearing member yet.
Recently, polymerization toners which are produced through polymerization process are placing on the market, aiming at higher image quality and low production energy. Those toners have excellent characteristics wherein particles have fewer angulate parts, and the particle diameters are small and uniform compared with toners produced through grinding processes. However, a disadvantage of those toners is that a cleaning step, employing a cleaning blade such as a rubber cleaning blade, during which the surface of the image bearing members is cleaned, tends to have cleaning failures because remaining toner components will not be easily removed as removing the remaining toner components will be affected by shapes and particle diameters of the polymerization toner that make it difficult to catch the components with the edge of a cleaning part of the cleaning blade pushed onto the surface of the image bearing member to contact therewith.
JP-A No. 2000-330441 proposes an example of a cleaning unit that can overcome the above-stated toner cleaning failures. It proposes an image forming apparatus which can give pressure, the pressure satisfies specific conditions measured on the volume average particle diameter of toner, D, and average degree of circularity, S. According to the proposal, strong pressure force, f, applied on a counter type cleaning blade, may cause noise generation and/or warpage of the cleaning blade, thus it insists that an empirical upper limit value should be set.
JP-A No. 2005-99125 proposes a cleaning unit wherein a friction coefficient of toner and an image bearing member, a friction coefficient of toner and a cleaning blade, an adhesion force of toner and the image bearing member, a force applied to toner given by the blade, and an angle between the blade and the image bearing member, or a cleaning angle, are specified, designed for removing particles having smaller average particle diameters and closer globular shapes.
The above mentioned JP-A No. 2000-330441 and JP-A No. 2005-99125 propose methods for reducing the stress on the image bearing member given from the cleaning unit while improving cleaning property at cleaning globular shapes toner, particularly as typified by a polymerization toner, however, they neither disclose or suggest method concerning prolonging the life period of the image bearing member while reducing the electrical stress applied thereon.
Thus, even tough protecting the surface of the image bearing member from electrical stress generated in the charging process is significantly important for prolonging the life period of image bearing members and charge members and for stabilizing image qualities, the protecting method is still in dispute and has many examinations on the methods yet to be made.